This application addresses the broad challenge area (06) Enabling Technologies and the specific Challenge Topic of 06-ES-102: 3-D or Virtual Models to Reduce Use of Animals in Research: Creation of Miniature Multi- Cellular Organs for High Throughput Screening for Chemical Toxicity Testing. Although toxicology tests have been performed using animals, there exists an urgent and critical need for alternative in vitro tests due to rapid changes in public views and regulatory requirements. Among many diseases caused by environmental chemicals, contact dermatitis is the leading disease in terms of the incidence - the CDC has listed contact dermatitis as one of the 21 research priority areas of the National Occupational Research Agenda (NORA). Because contact dermatitis is preventable by eliminating skin contact with causative agents, development of in vitro assays for identification of such agents has a broad and major impact on the global public health. Contact dermatitis is classified into irritant dermatitis (innate inflammatory responses to irritant chemicals) and allergic dermatitis (T cell-mediated adaptive immune responses to skin sensitizers). We have identified ATP release from keratinocytes (KCs) as an initial and causative event in the pathogenesis of irritant contact dermatitis. Because several different contact allergens are known to induce IL-1[unreadable] mRNA expression by dendritic cells (DCs) in the skin, we have developed a HTP-compatible DC biosensor clone by engineering our skin-derived DC line XS106 to express the yellow fluorescence protein (YFP) gene under the control of the IL-1[unreadable] promoter. Our objective is to develop a 3D multi-channel skin biosensor system that is composed of KCs, DCs, and fibroblasts (FBs) and that allows simultaneous detection of skin irritants (measured by ATP release) and skin sensitizers (measured by fluorescence signals). Under Aim 1, we will construct a KC biosensor clone by engineering the Pam 212 KC line to express the GFP gene under the control of Nrf2 (a transcription factor capable of triggering the Keep1-Nrf2-ARE cell survival response to environmental stresses). We will also generate a second DC biosensor clone expressing the DsRed gene under the control of Tfec (a transcription factor known to regulate cytokine and cytokine receptor gene expression). Under Aim 2, we will reconstitute a 3D skin model by: a) culturing the NS FB line in hydrated collagen gel to form a dermal-equivalent matrix, b) culturing a KC biosensor clone on the top of the collagen matrix, and c) seeding two DC biosensor clones to form a multi-cellular epidermal structure with KCs. Under Aim 3, we will test 18 skin irritants and 36 contact sensitizers in the resulting 3D skin model to evaluate the sensitivity and specificity. We will measure ATP release as an indicator of skin irritating potentials and YFP, GFP, and DsRed signals to identify and even classify skin sensitizers. Finally, we will improve the HTP capability by reconstituting 3D skin-equivalent micro- cultures in a 96 well-plate format. Once developed and validated, the 3D skin model with dual functionality may enable the industry to eliminate the use of animals for skin toxicology studies. Among many diseases caused by environmental chemicals, contact dermatitis is the leading disease in terms of the incidence. We will develop a three-dimensional, multi-cellular skin culture system to test a large number of industrial and environmental chemicals for their potentials to cause irritant and allergic contact dermatitis. Once developed and validated, the resulting 3D skin model may enable the industry to eliminate the use of animals for skin toxicology studies.